PC (i have done it on Windows 8.1+10)
Android Kernel Kitchen or similar tool
Photoshop,Gimp or Paint.net
Not much,the only is that u never ever change
the name and file end from the images.
1. First extract the recovery.img from your zip and place it were u want or in the folder from your Kerneltool.
2. Unpack it by drag and drop on the unpack option and wait till its done,now press enter.
3. Now go to ramdisk folder and open res folder and then images.
4. Make your changes and go away here.
5. Now press repack image and youre done so far.
The new recovery file is called image-new,just rename it to recovery put it in your zip and flash,enjoy!!!!!